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Message-ID: <4E6CC769.10604@squeakycode.net>
Date: Sun, 11 Sep 2011 09:36:25 -0500
From: Andy Colson <andy@squeakycode.net>
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To: Igor Chudov <ichudov@gmail.com>
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Subject: Re: Postgres for a "data warehouse", 5-10 TB
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On 09/11/2011 09:21 AM, Igor Chudov wrote:
>
>
> On Sun, Sep 11, 2011 at 9:16 AM, Claudio Freire <klaussfreire@gmail.com <mailto:klaussfreire@gmail.com>> wrote:
>
>     On Sun, Sep 11, 2011 at 3:59 PM, Igor Chudov <ichudov@gmail.com <mailto:ichudov@gmail.com>> wrote:
>      > Well, right now, my server has twelve 7,200 RPM 2TB hard drives in a RAID-6
>      > configuration.
>      > They are managed by a 3WARE 9750 RAID CARD.
>      >
>      > I would say that I am not very concerned with linear relationship of read
>      > speed to disk speed. If that stuff is somewhat slow, it is OK with me.
>
>     With Raid 6 you'll have abysmal performance on write operations.
>     In data warehousing, there's lots of writes to temporary files, for
>     sorting and stuff like that.
>
>     You should either migrate to raid 10, or set up a separate array for
>     temporary files, perhaps raid 0.
>
>
> Thanks. I will rebuild the RAID array early next week and I will see if I have a Raid 10 option with that card.
>
> Quantitatively, what would you say is the write speed difference between RAID 10 and RAID 6?
>

Note that using RAID 10, while faster, cuts your usable space in half. 12 2TB drives in raid 10 == 6 drives * 2TB == 12 TB total space.  That's not big enough, is it?

-Andy